In the UK, 29,000 people die prematurely every year as a result of air pollution - more people than are killed or seriously injured in road traffic accidents. We cannot waste any more time ignoring this invisible killer.

The government needs to live up to its legal responsibility to protect people. In London, more than 4,000 early deaths were caused by air pollution in 2008 - the same number that died in its famous great smog of the 1950s. Children are particularly susceptible to the effects of the many poisons in our air, and can suffer long-term health effects as pollution impedes their respiratory development. Despite these facts, successive governments have failed to confront the issue.

The case against the UK government is clear cut. Both UK and European Union law sets limits on air pollution levels based on World Health Organization recommendations. The government is required to produce plans showing how it will achieve legal limits for nitrogen dioxide by 2015 - but for more than one in three of the UK's air quality zones, the government has unlawfully drafted plans that far overshoot this deadline (in London's case until 2025).

Our case also challenges the government on its undemocratic refusal to consult Londoners on air pollution plans for the capital. The European Commission recently granted the UK a time extension to comply with legal limits for dangerous airborne particles on the condition that plans to deal with these particles are improved. The government was obligated to consult the public on this plan. Their failure to do this meant that UK citizens and air quality experts were denied the opportunity to highlight its errors.

A full consultation might have resulted in a more credible plan to tackle the issue. To reduce vehicle emissions before the Beijing Olympics, drivers were forced to stay off the roads based on the numbers on their licence plates - such draconian measures would be electoral suicide in London. The government should opt for a low emissions zone banning only the most polluting vehicles.

When it formed in 2010, the UK's coalition government promised it would "work towards full compliance with European Air Quality Standards". By refusing to meet their responsibilities on air pollution their claim to be the 'greenest government ever' is going up in smoke.

The pressure is growing - ClientEarth is not alone in calling attention to this issue, with Clean Air in London and Environmental Protection UK's Healthy Air Campaign also demanding meaningful action. Soon the whole world's eyes will be on London.